Malaria is a growing public health problem. Many countries in the Caribbean region that launched successful malaria eradication programs in the 1950s and 1960s are now experiencing sporadic outbreaks of falciparum an vivax malaria. These countries remain receptive to malaria due to their indigenous Anopheles mosquitoes. Currently, it is impossible to predict the potential for malaria re-introductions and epidemics because there is only limited, recent information on the status of anopheline mosquito populations and ecologic factors affecting site- specific receptivity for malaria parasite transmission. This proposal seeks to investigate how Anopheles mosquito species in Trinidad differ in their innate vector competence and natural potentials for parasite transmission The situation in Trinidad provides a good example of how malaria-free countries must now re-establish malaria surveillance and control operations in response to sporadic malaria outbreaks generated by an increasing number of imported malaria cases, including drug- resistant Plasmodium falciparum strains, from diverse areas of the world. Species of Anopheles mosquitoes indigenous to Trinidad will be experimentally infected with in vitro cultured gametocytes of P. falciparum, the most pathogenic human malaria. Parameters of parasite development for each anopheline species, determined by quantifying each major sporogonic stage over 20 days, will be related to infections in a reference species included in each experiment. Corresponding profiles of vector blood-feeding behavior and digestive physiology will be developed for each anopheline species. These studies will define Anopheles species differences in susceptibility and parasite development. Associated field studies will examine key aspects of vectorial capacity for natural populations of competent vector species to identify areas of Trinidad which are receptive to malaria re-introductions and potential epidemics. These collaborative studies on malaria vectors in Trinidad will provide opportunities for exploring how basic information on vector- malaria parasite relationships can be applied to strengthen malaria surveillance and control operations in the Caribbean region.